Currently available electromechanical cables are configured having a strength member external to the electrical conductors which is formed by helically winding a plurality of metal wires about the central electrical core, the helically wound wires covering approximately 95-98% of the outer surface of the electrical core. In order to achieve a torque balance and increase strength, two or more of these armored wire layers are sequentially laid over the electrical core. Attempts have been made to form the helical layers in directions opposite each other so as to achieve torsional balance of the entire cable. Usually this contrahelical construction is limited to two layers only, whereupon the outer layer having the larger moment arm and total material cross section generally has the dominating torque and torsional unbalance is caused to exist. A torque unbalance in an electromechanical cable, especially one which is suspended in water, is undesirable because it causes an angular twist in the cable around the cable axis which progresses as tension is applied to the cable by any means when the one cable end is allowed to rotate. A cable having this twisting tendency is subject to damage by various means including kinking and birdcaging which results when the restorative torsional energy of the long length of a cable is released over a relatively short length of the same cable. This local tensional energy release causes a sudden return rotation of the cable which loosens one layer of armor (usually the outer layer) of a contrahelically or double layer armored cable. This loosening causes the armor wires to locally form into a much extended diameter which results in a phenomenon referred to as a birdcage. With regard to kinking, the stored rotational energy within the cable causes several local cable rotations so that cable loops or coils result. Any subsequent tensioning of the cable without prior reverse rotation will result in tightening of the loop with consequent damage to the armor wires and/or the electrical cord.
Another major problem relating to currently manufactured electromechanical cables, with which the present invention is directed, is cable weight. Specifically, available armored electromechanical cables are fully armored throughout their entire length. As a result, that portion of the cable (usually the top portion of the cable) which supports the remainder of the cable has to support a fully weighted cable throughout its entire length. The strength inherent within the fully armored cable proximate the lower end of the cable (assuming the cable is hung vertically in water) has an inherent strength which is far in excess of that necessary for the support and electrical conductance of relatively light instruments. As a result, the final cable produced is usually of a size and strength which far exceeds, at least at its lower end, the strength necessary for supporting the cable at its lower end.
Another problem associated with currently available electromechanical cables is a limitation of the flexure life of the cable when the assemblage is traversed over a circular surface while the cable is held under tension. Such circular surfaces may include those on sheaves, capstans, winches and the like. Flexure life for currently produced contrahelically armored cables is limited to a value below 50,000 flexure cycles and more generally below 20,000 flexure cycles. Cable flexure life is limited because of the rapid wear of the metallic surfaces of the wires in adjacent armored layers which is caused by the very high compressive forces and poor lubricity. The flexure life will decrease as the ratio of the diameter of bend of the electromechanical cable to the diameter of the largest wire in the strength member assemblage decreases. This ratio in current art is above the value of 400.